Efficiency of Different Basic Modelling Approaches to Simulate Moisture Buffering in Building Materials

Carla Balocco,Giuseppe Petrone

doi:10.2174/1874836801610010561

Abstract

The aim of this study is the numerical investigation of the capacity of porous hygroscopic building materials to damp indoor humidity variations due to external environmental loads and internal sources due to heat and moisture exchange. By means of numerical simulation, building material moisture content is computed by using a basic approach based on a diffusion model. Subsequently, a model incorporating the isothermal sorption curves of materials and complete thermal analysis is elaborated. The first modelling approach is more appropriate for material characterization even though it requires more time for modelling implementation and involves greater computational costs. The second modelling approach is useful for the assessment of hygro-thermal behaviour and energy performance of complex building components made of different materials. Moreover, this second approach can be easily applied to a 3D solid model of complex geometrical and architectural layouts. Results involve two different geometries. The first geometry belongs to a 1cm sized cube and represents the test system used in our study. The second one is representative of a usual building wall with a thermal bridge, consisting of different layers. From results analysis, it can be deduced that a more accurate numerical approach, using thermos-physical properties, porosity and hygroscopicity of materials and their corresponding sorption isotherm curves as input data, could be proposed for material characterisation and hygrothermal behaviour evaluation, in relation to the real physical indoor and outdoor transient climatic conditions. On the other hand, in many practical technical applications, our two proposed approaches can comprehensibly describe the investigated process combined with building-plant system energy performances, depending on the implementation process and computational costs we can implement.

Highlights

Energy saving in civil applications is a subject of great interest and primary importance
Most of the literature has demonstrated that moisture buffer capacity of hygroscopic materials used in buildings influences the indoor microclimatic conditions for thermal comfort, durability and thermo-physical performances of material/envelope, indoor air quality (IAQ) and ventilation control and contributes to energy saving, due to operating hours and size reduction of the heating and ventilating air conditioning (HVAC) plant system [9 - 12]
We propose a comparison of results carried out by two different 3-D modelling approaches in order to simulate the moisture buffering in porous materials used for building applications

Summary

Introduction

Energy saving in civil applications is a subject of great interest and primary importance. A great deal of published research has shown the benefits from inside relative humidity variation control provided by hygroscopic materials [3 7]. Most of the literature has demonstrated that moisture buffer capacity of hygroscopic materials used in buildings influences the indoor microclimatic conditions for thermal comfort, durability and thermo-physical performances of material/envelope, indoor air quality (IAQ) and ventilation control and contributes to energy saving, due to operating hours and size reduction of the heating and ventilating air conditioning (HVAC) plant system [9 - 12]. It has been widely demonstrated that mould and microorganism growth on building surfaces and structural connections (e.g. thermal bridges) associated with high relative humidity levels of indoor air are connected to moisture exchanges and heat and mass transfer related to transient external and internal ambient conditions [13 - 15].

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